I-Firefox Isithangami Sokwesekwa

Some optimized mp4 do not play at all in any of my FF. From what I can see, this video is 10 fps and description says "Optimized using ezgif.com". Small and short videos. Lenghts seems to be correctly indicated by FF player frame.

All other MP4 play perfectly in any of my FFs. When I download such mp4 to my computer, VLC will play it normally. Any FF at this same computer will not! I repeat: all other videos play perfectly normal, including any MP4 I tried! Anything else on this same site plays normally. I am on Win 7.

I remove all security features I can, still, this single sort of videos are not playing and this is true for any such videos on this site. I tried 4 different versions of FF (v29, 60.9.0esr, v65 IceDragon, v71). They inherit configuration from the existing ones, so they are not clean installs. The same problem I have in several Win7 computers (two Virtual Machines and a real computer, not Win 7 N). FF safe mode does not help also.

Example page containing such mp4 with a cat: https://www.index.hr/lajk/poster/227148/vlasnici-su-snimili-svoju-smijesnu-macku-koja-se-moze-provuci-i-kroz-najmanji-prostor

and when I isolate just the video:

https://storage-lajkhr.index.hr/kiki/a727a5a6-734f-44d6-9ee8-42b857f22193.mp4

in FF I get only an empty black page and frame with player and no video at all.

What is wrong here?

In general, when downloading, authorizing on some sites, I have this problem - "Invalid redirect on page". Moreover, this error occurs only on the firefox engine, but not on chromium. I am writing from a browser Comodo IceDragon. The screenshot that I attached is in Russian.

First, I have no idea what I am doing re any sophisticated knowledge re Firefox or any other browser. So, please bear with me re how to understand my question.

I have no idea what I did, but after getting the latest Firefox, I cannot access Reddit. Let me explain: I was able to click on each topic/post freely on Reddit. Now when I visit Reddit, the topics/posts are stagnant and when I click on a topic/post, it goes to another page and I have to click on the URL to read the post. Also, if there are multiple pages on a post, the only page I can see is the first, I cannot click through to view anything additional.

It seems that Firefox is blocking Reddit. I hope this explains this issue.

Also, I cannot find the "settings" for Firefox now... to allow unlimited scroll and to automatically go to a new page.

Have set duckduckgo as default search engine but search just returns duckduckgo main page, not keyword search results when keywords are typed in search bar and hit search. If I revert to bing it shows results as usual. Change back to duckduck and it reverts to just showing duckduck main page again. Any suggestions